How do you kill white ghost slugs?

Question

The slugs cover our patio area at the rear of the house and the steps at the front.

Answer 1

I had never heard of Ghost Slugs and had to do a bit of research.
Identifying the they are indeed Ghost Slugs appears to be a difficult task...thus the name Ghost Slug. They live deep in soil and rarely come to the surface from my reading. They consume earthworms.
Many people mistake the Field Slug for a Ghost Slug.
Field Slug can be controlled with normal slug deterrents.
Best of luck and thank you for bringing me 'a new one'!

I'm listing an article for you and a link about slug control.
http://www.museumwales.ac.uk/rhagor/article/ghost_slug_2014/
https://www.gardeningknowhow.com/plant-problems/pests/insects/kill-garden-slugs.htm